In a mine or other environment wherein communication is required among different regions, a transceiver located in each region is electrically coupled to a pair of phone lines that extend throughout the mine. The phone lines carry voice signals that are coupled between handsets during a push-to-talk mode of operation. During a push-to-page mode of operation, the voice signals are reproduced in a loudspeaker at the called transceiver.
A typical paging intercommunication system of the prior art is shown in Shields U.S. Pat. No. 3,941,933. Each transceiver is contained within a housing having a cradle supporting the handset and is electrically coupled to the signal lines through a connector. A speaker mounted within the housing broadcasts voice signals during paging under control of the calling transceiver. The handset contains a push-to-talk switch for coupling voice signals from a handset microphone onto the lines to be reproduced in the earpiece of the handset of the called transceiver. Mounted on the housing of the transceiver is a push-to-page switch that when depressed applies a d.c. voltage onto the phone lines to energize the loud speaker circuit of the called transceiver for paging.
One disadvantage of the prior art paging intercommunication system of the type shown in the Shields patent is that when the paging mode of a transceiver is operated (this is done by simultaneously pressing the push-to-page and push-to-talk switches), the paging amplifiers and loudspeakers on all transceivers coupled to the line are activated. Thus, the voice signal generated by the caller is reproduced simultaneously through the loudspeakers of all transceivers even though the page is relevant to only one transceiver in the system. As a result, battery power consumption is relatively high. Battery power consumption must be minimized, however, in a mining environment to increase system operating time as well as improve system reliability. As another disadvantage of the prior art paging intercommunication systems of this type, because paging is made through all loudspeakers, frequent paging is annoying to personnel and reduces attentiveness to the paging signals.
In order to provide a selectivity capability to paging communication systems whereby only a preselected transceiver, rather than all transceiver units coupled to the lines, is actuated to receive paging signals, addressing systems using conventional telephone rotary or TOUCH-TONE dials have been developed as shown in McIntosh U.S. Pat. No. 3,971,899 and Marshall U.S. Pat. No. 3,909,551. In the Marshall patent, rotary dial pulses are counted and converted into binary coded decimal (BCD) form representing the dialed number. The BCD data are supplied to operate relays that steer a ringing signal to the called station addressed at the rotary dial. In the McIntosh patent, steering circuitry responsive to either rotary dial or multi-frequency tone signals addresses preselected stations based upon either single digit or two digit codes.
Although battery consumption is thereby reduced, there is a tendency for the paging mode to be overused by the caller. In a mining environment, for example, the called party is frequently not available for immediate reply to the paging signal. The calling party thus tends to repeatedly page the party or to repeat the page at relatively short time intervals until the page is answered. In order to further reduce battery power consumption, it is necessary to limit use of the paging mode within the communication system while retaining the paging function.
One object of the present invention, therefore, is to provide an improved paging and intercommunication system wherein battery power consumption is minimized.
Another object of the present invention is to provide an improved paging and intercommunication system wherein battery power consumption is reduced compared to that of the selective paging and intercommunication systems of the prior art.
Another object is to provide an improved paging and intercommunication system having reduced battery consumption that can be added to existing transceiver systems.
Another object is to provide an improved paging and intercommunication system wherein battery consumption is minimized by eliminating the requirement of repeated or lengthy paging when the called party does not immediately respond.
Another object is to provide an improved paging and intercommunication system that is operable with virtually an unlimited number of transceiver stations.